There are strong demands for reduction of the size and/or the thickness of piezoelectric devices used in information-communication equipments and other equipments. The developing side has responded to such demands through development of various sorts of piezoelectric devices that are intended for reduction of the size and/or the thickness.
Basically, a piezoelectric device is composed of a piezoelectric resonator element, an electronic component such as an integrated circuit (IC) that performs temperature compensation, resonance control and/or other operations for the piezoelectric resonator element, and a package in which the piezoelectric resonator element and the IC are packaged.
As shown in FIG. 3, a common structure of a piezoelectric device that is intended for a reduction of the size includes an IC 3 placed on the floor of a package 4 that is formed in tiers and a piezoelectric resonator element 2 placed on a tier over the IC 3. In such a structure, however, it is necessary to provide a resonating space for the piezoelectric resonator element 2, while also providing a clearance between wires 5 for wire-bonding to package the IC 3 and the piezoelectric resonator element 2. This causes a major problem in reducing the thickness of a piezoelectric device 1 having the structure described above.
On the other hand, among piezoelectric devices that are intended for reduction of the thickness is one disclosed in Patent Document 1. As shown in FIG. 4, in the piezoelectric device disclosed in the document, supporting portions (protrusions in Patent Document 1) 6 are formed inside the package 4 to serve as supporting portions for the piezoelectric resonator element 2, and the piezoelectric resonator element 2 is placed side by side with the IC 3. Such a structure of a piezoelectric device allows a height-lowering of the device by precluding the necessity to allow for a vertical clearance between the piezoelectric resonator element 2 and the IC 3.
The piezoelectric device disclosed in Patent Document 1 is inferior in size reduction, but superior in thickness reduction, to the one shown in FIG. 3. Furthermore, since the piezoelectric resonator element and the IC can be mounted simultaneously or serially in the package, the process of hardening the adhesive used for mounting the two components can be performed at a time as one common process, an advantage that allows an improvement in the productivity. In addition, packaged conditions of the two components can be checked by observing from the surface, even after they have been mounted.
[Patent Document 1] JP-A-H9-83248
Both the piezoelectric device shown in FIG. 3 and the one disclosed in Patent Document 1 may be very effective in reducing the size and/or the thickness of the device when an AT cut or other quartz crystal resonator element is employed as a piezoelectric resonator element.
However, generally speaking, the piezoelectric device in FIG. 3 and in Patent Document 1 are not suitable for use in cases in which a surface acoustic wave element (SAW element) is employed as a resonator element, a SAW element being thicker and heavier than an AT cut or other quartz crystal resonator element. Both of the piezoelectric devices shown in FIGS. 3 and 4 have small supporting areas for a resonator element. Therefore, when a weighty SAW element is mounted, the resonator element undergoes the risk of being deformed by its own weight. It may also be possible to draw upon the piezoelectric device shown in FIG. 4 as a guide and provide adequate supporting areas for the resonator element by placing the element and the IC on the same level. However, this tends to deform the package itself because the package floor of the piezoelectric device shown in FIG. 4 is thin. Thus, the SAW element supported by the package floor is likely to be affected by deformation of the package.
An object of the invention is to provide a package structure for a surface acoustic wave device and a surface acoustic wave device that realize a reduction in the size and/or the thickness and that is suitable for packaging a surface acoustic wave element.